The present invention relates to a method of processing finely divided bulk material with gas without overpressure. The invention also relates to an apparatus for carrying out the method.
The method and the apparatus according to the invention may be used for processing finely divided or flocculent material in general, but has especial utility in the wood pulp and paper industry.
It is to be understood that when a finely divided pulp is referred to in the following, this term is meant to include both mechanical and chemical wood pulp.
In the wood pulp industry it is known to process a finely divided pulp originating from certain types of wood, e.g. fibres of hardwood, with ozone. As a consequence of the ozone process, the fibres of the pulp may be more easily bonded to each other at a later stage of the production process. Since the hardwood fibres are smaller than fibres originating from coniferous trees, they are well suited for mixing with conifer pulp in the production of fine paper, and also in this connection the processing of the hardwood fibres with ozone is favourable for the final paper product.
Thus, the ozone processing is an important step which enhances the strength of mechanical wood pulp, i.e. mass produced by mechanical fibration (grinding/refining) of short-wood or chips.
Further, in the pulp wood industry the use of ozone in bleaching chemical wood pulp, i.e. cellulose, is known. By bleaching the cellulose mass with ozone, the use of chlorine is avoided, which is favourable with respect to pollution.
However, from the literature there are only known apparatus for processing finely divided wood pulp in which the gas is allowed to penetrate into the pulp under overpressure. In processing such pulp with pressurized gas it is difficult in a simple manner to recover the surplus of gas for recirculation. Besides, the processing of a pulp with pressurized gas will easily result in a compression of the pulp to be processed, requiring the pulp to be moved through the reactor by complicated and expensive devices. Apparatus for processing pulp with pressurized gas are therefore unduly expensive and poorly suited for a process using no overpressure of the gas, especially since large gas volumes must in this case be separated from the pulp.